Automatic flight controller



Sept. 30, 1952 R. l.. FRAzn-:R ET AL AUTOMATIC FLIGHT CONTROLLER 11 shets-sheet 1 Filed March 19, 1947 R. L. FRAZIER ET AL AUTOMATIC FLIGHT CONTROLLER S'ept. 30, 1952 ll Sheets-SheeiI 2 Filed March 19, 1947 E 0% WWW MW n Ma E BY Sept. 30, 1952 R. L. FRAzlER ET AL AUTOMATIC FLIGHT CONTROLLER ll Sheets-Shee'I 5 Filed March 19, 1947 INVENTORD.

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AUTOMATIC FLIGHT CONTROLLER Filed March 19, 1947 ll Sheets-Sheet 4 BY "i We.

Sept. 30, 1952 R. L. FRAZIER ET AL AUTOMATIC FLIGHT CONTROLLER ll Sheets-Sheet 5 Filed March 19, 1947 .E www M ma M i Vf; .y my. J W Z@ w WMZ@ i INVENToRs. M42/@y f @6x4-24m@ aaall Sheets-Sheet 6 BY ,er 5642/56 1&1

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Il' Yf/ Sept. 30, 1952 Filed March 19, 1947 Sept. 30, 1952 R. FRAZIER ET AL AUTOMATIC FLIGHT CONTROLLER ll Sheets-Sheet 7 Filed March 19, 1947 Sept. 30, 1952 R. 1 FRAzlER ET AL 2,612,331

AUTOMATIC FLIGHT CONTROLLER Filed March 19, 194'? ll Sheets-Sheet 8 7a ,Ff/005e (aA/feaLs M44,... @Wam Sept. 30, 1952 R. FRAZIER ET AL 2,612,331

` AUTOMATIC FLIGHT CONTROLLER Filed March 19, 1947 ll Sheets-Sheet 9 ,605567 Fraz/5e BY Sept. 30, 1952 R. L. FRAZIER ET AL AUTOMATIC FLIGHT CONTROLLER 1l Sheets-Sheet lO Filed March 19, 1947 L tflllln mmf SePt 30, 1952 R. L. FRAZIER ET AL 2,612,331

AUTOMATIC FLIGHT CONTROLLER Filed March 19, 1947 ll Sheets-Sheet ll 505567724. FEZ/E@ BY l Patentecl Sept. 30, 195.2

UNITED vSTATES PATENT A Robert Frazier, St. Louis, Mo., and Harry Bi i Breedlove, Baton Rouge, La.v 1f: fla

pnlicatfionMarh 19, 1947, serial No. "735,590( j 24 Claims. `(c1.v 244-77) (Granted under the act of March 18.83, as v 4amended April 30, 1928; 370 Q.YG. `757)v der, ailerons, engine throttle, Wing flapsand wheel brakes. i i

Another object of the vention the :provision of aircraft control means automatically ,operative for landing an aircraft .under .conditions of zero visibility. Blind landing .'systemsusually depend on the interpretation of signals .by .the airplane pilot and .are thus subject to human error in misinterpretation orflack of attention. However'by providing. an aircraft control system whereby the flight 4sequence is predetermined and the approach and landing is effected by automatic control any failure rcan .only-be of a mechanical nature.

A related object of .theinvention is .to .provide in combination With an aircraft,` .an .automatic gyropilot and control apparatus `connected to the gyropilot for effecting automatic `flight .over a vpredetermined course and in .-accordance With a predetermined flight plan starting from one lairfield and 'landing at another .aireld.- specifically it is intended thatan-.electrlcal.gyropilot bev connected through its signal system :with a combination of electrical vsignal producing de.- vices capable of feeding signals `to the gyropilot 'to effect .appropriate and coordinated aircraft control. `Besides providingcorrect aircraft :heading at each stageof .the aircraft flight, :it :is desired to obtain controlled .up .and downfmovements of the aircraft as well as Ato-hold the-air.

rectional control of the aircraft by applying to.

the electrical gyropilot ;a -radiocompass'signal output having directional characteristics according to the orientation of .theaircraftWith-respfwt Zivi..

- to a direct course toward a nondirectional radio l the proper time, the control apparat-his` Gatien t0 .existing aircraftthe-prior art Systems, i invention t0 imnl'oregthe Aand precision .of automati tems and System .comnmientsyhel variations -in .the :flight rplanlwill .in the. detailed description.'

A further object of the invention. is. te Prev-ies an aircraft control apparatus including a sequentially operated Switching devieasiepisd t0 close a group of circuits at each step of the switching device .S0 este .etat @Ort-r0.1. ever a plurality of .aircraft .9Qril'fr91relemeeisai @e911 Stage 0f a planned flieht Accordingly .1er-rrevldifnsautomac devices i0 regie the. witch-ing device imm each sequential .siente he completely automatic .fremtari .te wh..

A11 .important Object pi.,-the'-invntzien .riesiges in theprovision of Ameans to vc n g of an aircraft automatically upon-la -v f by. the application gf the brakes. 994513.@ left and right Wheels vwill not only ing theeraftfto va stop but will also act to guide `1t along va runway 0r landing-.field- Inghidsd le Qontrol combinati@ ineens is .aerwide i0 Slow the aircraft ,doive .gradi-rallyes@ et. Steady wie 0f deceleration Another important Obi iris .t .0i/isle a 9ev0f diifaiecland.fully antenati@ e' Qeirflsrstem for an aircraft with.. er. r Veltins throttle orpoWer settings Icite l engine @refranes accorsim 'td a ...s and template YJalan adapted f9.1 yal-V sa Automatic.. aircraft. .Central Systems leavereviplislr .been procese@ es for iris ent NO.- 2.322.225 to C appreciationof the me ASpecifically it is 4an' object. of .ithe :invention -to yprovide a .completely coordinated aircraft 'control system which will control all the operating units of a modern aircraft, the system including control means for the aircraft engines, 1 orv4 the aircraft control surfaces, for the vvi'n retractible landing gear and for Wheel brakes. The complete to the invention provides a quential operation of the lva trols conforming to a .desirablean I -considered night plan. Mdreever the"'system er the invention is .flexible enough .Ito l.maire possible variations of .any single ,night plan. .Possible be .pointed .out

The. inventionconsists` substantially @thereonstruction, combination, location and relative arrangement of parts and circuits for obtaining the results desired in accordance with `the objects of invention stated above, or as'implied in the detailed description or in the claims.

The above stated Vand other objects of invention will become apparent on reading the following detailed description and claims inconjunc tion with the drawings, in which: .l

Fig. 1 is a diagrammatic view oi the aircraft control .system showing the coordinated hookup of the various aircraft control units.

vconnection tocoordinate selector actuation, as

' representedvby the devices connected to contacts Figs. 2 and 2a together form a self-explanatory i diagram of the predetermined flight plan as accomplished by use of the present aircraft control system. l Y

Figs. 3 and 3a together form a wiring diagram of the present aircraft control system..

Fig. 4 is a vcombined electrical and mechanical diagram of the power control portion of the system. f

Fig. 5 is a combined electrical and mechanical vdiagram of the brake control portionof the system.v Y

' Fig. 5a Villustrates a modification of the system shown in Fig. 5. Y

Fig. 6 is a schematic view of the automatic air speed control device forming part of the power controlportion of the system. Y

Fig.v lis-fawiring diagram ofthe radio compass andr'adiocompass coupling forming'part of the system."` d y Y Fig.`8 is a perspective view of the forward end portion vof an airplane fuselage to show the antenna installations yemployed with thefpresent aircraft control system. j Y 1 y Fig. 9'is a diagrammatic view of theautomatic pilot' which yforms an essential unit of the airicraft control system. y

Fig. -10 is a wiring diagram of the automatic pilot as used with the present system. I

T heessential units which together form the aircraft control system are shown in Fig. 1 and in order to show these'quence of operations or stepsformirlg the system, the automatic or masf terfsequ'ence selector is shown diagrammatically and indicated by numeral I. The details of the lactua'lsequence selector will be discussed below but' as shown in Fig. 1 the selector is illustrated as providing means to initiate a desired sequence ofv aircraft control operations by providing' electrical connections to the` respective controll units.

` -At the left of the selector I is shown the means to initiate the sequentialsteps from 1 to 8 and at the right of `selectorlV is shown the control merated in response to various mechanical or 1 electrical impulses to which the devices respond.

`on the smaller arc, with selector circuit cony nections, as represented by the devices connected to contacts on the larger arc.

Line A extends down to the right to indicate coordination of the constant altitude control unit of the automatic pilot, whichas' indicated becomes effective at selector stations 3, 4 and 6.

There is also one intermediate step in the flight plan coming between points 5 and 6 but this step does'not'frequire a'separate station onthe master sequence selector, although there is no reason why the system could not be modified to add this vadditional point on the master sequence .selector l. Actually however it was found to be satisfactoryto produce this intermediatev step 51/2 by using an 'air pressure actuated switch B controlled by the pressurestatNo. l. In the final approach I of the aircraft from a cruise altitude vthe approach glide is maintained down vover from anlautomatic pilot down signal to the constant altitude control of the pilot and simultaneously lowering=the r`landing gear Vvand Vwing ilaps. The ,constant'ialtitude control of the automaticpilot isv an air pressure responsive device acting to hold the aircraft in level flight at whatever altitude the control isV cut-in. It will be seen that the fth phase or step of the flight willrthus be a steady glide Afollowed by a period of 'level ifiight .atlapproachaltituda While the cruise altitude was selected at 4000 feet and the approach altitude was'` selected as 1000 feet'it should be understoodA thatthese are arbitrary gures subject to change by proper selection of pressurestats and these altitudes Yin no way formj operational limitations of the' present aircraftV control system. I I

In order to .simplifyFig l'the constant alti, tude controL'the localizer control, the brake e011-,

-trol.and the'pressurestat No. 1 are shown twice :but in the system as actually wired'in complete willnow be explained in detail, and at` the same time referencewill be made to Figs. 2 and 2a to illustrate the sequence steps as they apply to the 'iiight plan ofthe aircraft and to ground installations Which-furnish impulses directly affectingthe radiocompass, marker beacon receiver, localizervfreceiver and ,glide path receiver.

Thefsteps.areasfollowsp steps of the sequential flight plan 1. Take-'off Y With the aircraft stationary on the ltake-off runway and lined up with the runwaythe engine is started and warmed up at idling speed by means of manual control devices,Y and the sequence selector being vatlzero or no-circuit station the aircraft control system is not yet in operation except that the electric power supply is turned on. However on actuation ofthe push button or flight starter thesequence selector stepping circuit is'. closed to step the selector to point L1 to actuate vthe brake control.' the power control and the up signal for the auto-pilot. The brake control. circuit. 'in this phase includes timev delay relays so as to hold the brakes set for `about eight seconds lafter the selector reaches step l. The power'control at step 1 results inthe'jap'- plication of'full throttle to give a maximum takeoff power and for purposes of illustration and comparison this throttle setting may be stated as giving 'a manifold pressure of 46 inches of mercury. For take-off an up signal is fed into the auto-pilot to give an angle 'of kascent of about 5 degrees. The manner in which the autopilot effects aircraft control will be explained in some detail below.

2. Steady climb After take-off the aircraft climbs rather sharply from the runway to an elevation of 1000 feet, or any other preselected elevation, at which time the pressurestat No. 1 actuates ay switch which again closes the selector stepping circuit to move the sequence selector to point 2. The circuit thus completed maintains'the up signal to the auto-pilot and closesathe landing gear servomotorand wing flap servomotor circuits to raise these elements into their full flight positions.

Also the power control setting is reduced to a more moderate value, in the presentvexample to aboutl 35 inches of mercury at the intake manifold. An alternative handling of the landing gear may be used if desired by connectingV the landing gear servomotor through a time delay relay for operation as part of step 1 or take-off phase. Under .this modified plan the relay has a setting of ten seconds or more to allow ample time for clearing the ground before actuation of the landing gear motor. This modification will afford less drag during initial climb and result in more power for an increased rate of Climb.

3. Navigation o1' cruise The steady climb phase proceeds until the aircraft reaches an elevation selected or possibly dictated by air traffic regulations. For purpose lof illustration this has been taken as 4000 feet and the pressurestat No. 2 is actuated at this elevation accordingly, closing the sequence selector stepping circuitv once more to step the selector to point 3. The circuits completed at Athis step cut in the magnetic heading control of vflight'` at minimum fuel consumption. This value maybe stated' in-the present examplefto be so'inches of mercury manifoldl pressure.

6 A v 4.1 Initial approach Cruise conditions" are maintained until the air logV dev-ice;4 runs to its preset point to close a switch whichy again operates the sequence selector stepping circuit to move the selector to point The selector then serves to close a circuit to a .motor operated tuning device which tunes the radio compass to a preselected Wave length'. The compass. signal is passed through the automaticapproach coupling unit to the automatic pilot, thus providingan accurate heading ysignal tosteer the aircraft toward a nondire'ctionalradio beacon (No. 1) of a known wave length corresponding to the setting applied to the radio compass by the tuning device. 'Ifhe automatic approach coupling to be described more fullybelow is a unit connected to the autopilot and which is capable of delivering a phase shifting alternating current to the auto-pilot in response to an input of low voltage direct current`of changing polarity, as delivered by the radio Icompass or bythe localizer and glide path receivers to be referred to below.

The vradio compass which receives its signal fromI a nondirectional radio beacon is shown in Fig. 7 `and as used in the present system requires a special coupling circuit which includes a vacuum tube. The twor antennas indicated in Fig. 7=are shown lalso in Fig.'8 as they appear on the aircraft. The loop antennaY is of the fixed type, having its plane at about a right angle to the longitudinal axis of the aircraft. The sense antenna, which does not have the directional elTect inherent in the radio compass loop, is mounted-under the aircraft fuselage. In addition to using the output of the radio compass to actuate a left-right indicator, the present system uses the output to hold the auto-pilot on a steady homing course, thus correcting for wind drift or other inaccuracy in heading during the prolonged cruise sequence.

As 4shown in Fig. 1 the constant altitude control is also used inthe initial approach phase (step 4) of the flight plan. The powerv setting forJ cruise is also maintainedv during initial appreach, manifold Ypressure being'SO inches of mercury.

, y5. Finallapproach I Accuratey heading at cruise altitude and cruise power setting is maintained until the aircraft comes within the cone-like signal field set up by the Z-marker beacon, which is ai type of radio beacon and in the present system is located at or` close to the nondirectional radio beacon No. 1. The Z-marker beacon is. commonly used in airways control work to provide an upwardly radiating signal marking a nondirectional beacon or radio range beacon and providing a signal response within the cone of silence existing over a beacon station. The signal picked up by y the Z-marker beacon is used' to actuate the sequence selector stepping circuit again through a relay circuit, to step the selector to point 5. The circuits thus completed by the selector are the radio tuner-radio compass-automatic aD- vpreach coupling-automatic pilot circuit, the

power setting circuit, and through switch B a circuit is also completed to feed a down signal to the automatic pilot. At this time however switch` Bis connected through the contact a thereof-' The glide angle is such that the rate of descent is between 400and 500 feetper minute, although the vrate" may run as-high asGUO 'feet per minute. The glide angle may be vari'edconsiderably by properadjustment of the down signal and power control. In this phase of the ightthe power setting selected may be stated by way of comparison as 22 inches of mercury,

manifold pressure. It is in this glide phase that the automatic air speed control unit of the power control is mostv important; proceeds until the pressurestat No. 1 responds at about 1000 feet to moveswitch B to contact b thereof. This contact closes a circuit to the conetant altitude control of the auto-pilot and at the same time disconnects the auto-pilot down signal. A circuit is also closed to connect the landing gear and wing iiap servomotor to a power source, thus lowering these elements to normal approach position.

ByV reference to Figs. 2 and 2a the nondirec- -tional radio beacons will be noted, being two in number. During the initial approach phase or sequence step 4 the aircraft will home on beacon No. 1, while during final approach I the aircraft will home on beacon No. 2. In each instance the directional control is by means of the radio tuner-radio compass-automatic` approach vcoupling-automatic pilot hookup. The beacons being on diiferent wave lengths the auto-pilot will re- The approach glide ceive a directional signal from only one beacon at a time. The tuner is built to tune the compass to several different wavelengths or channels, the tuning actionbeing accomplished by closing various circuits each affording a tuning action of a definite extent. The'motor of the tuner isv cut off after the proper movement is obtained and the radio4 compass tuning condenser is stopped exactly at the selected setting.V The construction of Vthese electro-mechanical .Y radio tuners is well-known, and no purposewould 'be served by complete illustration thereof.

6. Final approach II The constant altitude portion of sequence Y step 5 will. continue until the outer marker beacon is reached (this being also the approximate location of the second nondirectional radio beacon). At this location the marker beacon radiates upwardly a fairly extensive signal iield having a general balloon-like shape, as indicated in Fig. 2a. 'I'he marker beacon gives a signal to a marker beacon receiver on the aircraft, the receiver being connected to the sequence selector stepping circuit to step the selector to point 6. The selector now .makes connections effective to hold the constant altitude control unit in operation, to hold the power setting of final approach I in effect (22 inches of mercury manifold pressure), and to connect the localizer receiver signal to the auto-pilot through the automatic approach coupling. 'I'he localizar receiver picks up signals from a standard runway-localizer station located beyond the runway and on the axis thereof. The signals from,` the station are as usual mechanically modulated to twov different frequenciesof 90 and 150 cycles and are radiated by an antenna'array to form two elliptical signal fields overlapping in a narrow zone coincident with the axis of position.

7, Final approach III The constant altitude approach phase is maintained until the aircraft reaches the inner marker beacon' at which time the marker beacon receiver will actuate the sequence vselector stepping circuit to step the selector to point 7. With the selector in this position circuits are completed to the power control unit, to the localizer receiver and to the glide-path receiver. The two receivers are of course connected to the auto-pilot through the automatic approach coupling, as indicated in Fig. 1. The power setting will be reduced to about 16 inches of vmercury manifold pressureifor the approach glide, and the glide angle as determined by the glide path controlV will be about 2.5 degrees. The localizer lreceiver will hold the auto-pilot on a runway heading, as in the final approach II.

'Ihe glide path signal which is ordinarily fed from the glide path receiver to an indicator having a normally horizontal needle for visual aid in holding the aircraft on the correct glide path, is appli-ed in addition in the present system to the auto-pilot through the automatic approach coupling. By this arrangement the autopilot can be made to hold the aircraft on the correct glide path automatically. For a discussion of the standard glide path and runway-localizar control systems for instrument approach and landing reference may be had to Principles of Aeronautical Radio Engineering by P. C. Sandretto (1942) pages 168 to 197, published by McGraw-Hill Book Company. The antennas lgineering Handbook by Keith Henney (third 8i `Landing The glide approach tothe runway is continued until the nose-wheel and main wheels touch the runway. The aircraft weight is then taken by the wheel struts, which are made of two telescopic sections forming hydraulic chambers to permit absorption of landing shock. The struts themselves shorten in absorbing shock and consequently the hinge point of the two links used to prevent relative rotation of the strut sections (Fig 8) moves away from the strut. By means of a Bowden wire connected fromvmicro-switches to the hinge point of the links the micro-switches` are opened to again actuate the sequence selector stepping circuit,l stepping the selector to point 8. The selector in this position closes circuits to hold the runway-localizer control, the glide path control and to initiate the brake control through a time delay'circuit. The brakes are applied after a time interval of four seconds and the brakes are applied differentially in the twomain wheels by means of a follow-up control operated bythel rudder cables. This combination of controlls acts to guide the aircraft along the runway in response `to the runway-localizer control. The selector also completes a circuitto select a new power setting for idling, thel manifold pressure at this time'being inthe neighborhood of inches of mercury. The glide path control is useful even after touchdown, since the standard glide path receiver includes an alarm circuit utilized in the present system to feed an up signal when the glide path signal eld has been passed. By this control actionvthe tail of the aircraft is held down for a smoother, safer landing. j f

Master sequence selector 10 tinuously engaged by a brush 4a to 47', to which may be soldered a conductor. Thus each station or point on the sequence selector may be arranged to close a separate circuit for 'each selector gang present in the sequence selector. For instance at station 1 the gang Ic closes a circuit from ground to brush 4c, to plate 3c, to contact I of gang Ic andthence by a vWire to magnetic relay REI-3 and also to time delay relay TR-l (Fig. 3a). The 0 station'of the sequence selector is used as a no-circuit or idle position, the selector normally occupying this station when the control system is not in opdisk there is a metallic plate keyed on the shaft and having a spring finger adapted to engage only a single conta/ct' of the adjacent disk at a time. The twelve positions of theswitch vcorrespond to twelve contacts secured to the periphery of each disk. Thus various circuits may be completed through contacts to the metallic plates, each of which forms a common'terminal for the individual selector gangs. The selector shaft extends beyond `theselector gangs at one end to a selector stepping device" which operates to engage a ratchet wheel keyed -on the shaft,

to step the selector one step ata time. The other end of the selector shaft is'extended through a control panel and carries thereonv a l pointer and a knob. The pointer is adapted toindicate on the faceof the. panel the position of the selector at all times. lThe knob is useful to step the selector from the last active step (point 8) around to the beginning (point 0)`y preparatory to take-off. ve While the details'of the sequence selector form no part of the present invention, the stepping device for the selectormay be described as a short stroke solenoid or electromagnet, the armature of which carries a'dog or tooth engageable with the ratchet wheel to step the selector only one step ata time in only one direction each time the solenoid circuit is closed. The actual details of. the selector' maybe Varied, but the above description should conveya clear understanding of the type :of'switchfreduired and even the construction which may be used. A similar type of switchhaving fewer contacts is disclosed in the patent to nCrane et `al- (Fig. 16a) referredto above. y v

ln Figs. 3 and 3a thewselec'tory drive shaft is omitted but as inthe actual switch a separate contact means is shown at the left hand side of eachdisk for continuous' contact with the associated central plate having a contact nger thereon. Referring to Figs. 3 and-3a the separate selector gangs of sequence selector I are indicated .by numerals la to Iy' respectively. The insulating disks 2a to'27 carry the peripheral sets of equally spaced contacts which may be designated by the selector stations, numbered O to 11, These contacts are engageable 'by the spring fingers on the separate gang plates 3a to 37', the plates being driven together as a group by a central shaft which is insulated from the plates to prevent crossconnections between the separate gangs. Each of the plates 3a to 3j is con- Aso eration. l Y

, As shown in Fig.` 3 the sequence selector is adapted to be rotated one step at a time by means of a stepping circuit SC. The stepping circuit includes a solenoid which is adapted to be supplied with a 24 volt potential through actuation of a relay included in the stepping circuit. The solenoid has an end portion which by engagement with a ratchet wheel on the selector shaft is adapted to step the selector from one point to the next with each actuation of the solenoid. y

' Control system circuit Referring to Figs. 3 and 3a for a wiring diagram of the present controlv system, the arrangement of selector gangs, relays and .switches is shown whereby the various units making up the control system are connected into a complete and integrated flight controller. Also shown diagrammatically in Fig. 3a are the marker .beacon receiver coupling MBRC and the air log device, comprising air log spinner ALS and air log counter ALC. Some of the circuit lines extend from Fig. 3 to Fig. 3a land will be identified hereinafter as trunk lines I to I5. All magnetic relays are designated by the symbol RE and in each instance they are illustrated in a position when the relay holding coils are not energized. The separate selector gangs function to complete various circuits, some being exclusively identi,- fied with certain parts of the system. For instance the gang I a. governs the power control circuit, gang le governs the selector stepping circuit, and gang I7' governs the selectorstation indicator. Y

The circuits completed by the rst and last gangs may be disposed of at this point by stating that the circuits for gang la are described in detail under the heading of Power control hereinbelow. The gang I9' merely serves to connecta series of signal lamps located on the system control panel, so as to indicate by a single lamp for each selector station the particular station or point in effect at any time during` the iiight, thus giving the night engineer a means of checking on the operation of the selector. The circuits which are completed at each step of the selector will now be described in separate paragraphs numbered from 0 to 8.

0. The zero point of the master sequence selector provides no circuits through the selector gangs since the plate contacting` brushes lal to dy are located at this point, and the spring ngers on the plates will 'also be at the zero 1. The. selector having. reached point 1, the. v

, gang Ic makes a ground circuitthrough relay source through the trunk line 8, relayRE-t,

the trunk line 9 and thence to ground through relay RE-G. The electric power supply having been connected to the system vseveral minutes prior to initiating the. system control, the.v relay TR-Z' has ample time to' reach closed position since both time delay relays (TR-I and TRf-Z) have a time factor ofA four seconds both on closing and opening. Both` of these relays are also of the. normally open type, that is with the heating coil or timing element `deenergized the relays make no circuit connections. With. brakev terminals BR-I and BR-2 connected together the brakes are set while the engine turns up to full power, take-oli or maximum power having been applied by means ofv selector gang Ia.. At the same time the brake terminals are connected together, a circuit is completed to the heating coil of time delay relayA TRA-I by means` of trunk line 5 which is grounded through selector gang Ic. After four seconds the relay TR-I closes to complete a 4circuit to the holding coil of relay RE-6, the latter relay assuming an upward position to break the ground connection to trunk line 9. The 24 volt circuit of the heating coil of time delay relay TR-Z is now open and the relay itself opens in about four seconds, thus breaking the circuit between brake terminals BRFI and BH2-2 to release the brakes accordingly. Because of the additive effect of the two time delay relays the brakes are thus. held for eight seconds after the selector reaches point 1. The selector gang Ih makes a circuit from terminal I of terminal block TB-2 through trunk line II to the selector gang and thence out onl trunk line 6 vto relay RE-Z and on to the up signal source, comprising the upper half oi re.- sistance bridge circuit RBC. Thusv through the terminal block 'TB-2 an up signal reaches. the auto pilot, the circuit completed through the selector gang Ih .being equivalentto closing the manual switch SW-3 on the UP contact as shown. Since power as supplied by the. engine to the propeller is now full on the aircraft proceeds down the runway andtakes oft. The autopilot is so constructed that it holds the aircraft on the correct runway heading, so that the takeoi proceeds with correct runway orientation. This feature will be explained further under the section entitled Automatic pilot.

2. When the aircraft has reached an altitude of 1000 feet the aneroid switch PS-I closes, to energize the holding coil of. relay RE-I. This relay closes a circuit from ground to point 1 of the selector gang le and thence through the gang connections to the relay of: stepping circuit SC. The relay then closes to actuate the stepping circuit solenoid and move the selector to point 2. At point 2 the gang Ib makes a circuit from ground to the holding coil circuit of relay RE-I, to hold the relay contactors in the upwardv position regardless of the circuit closed by the aneroid switch PS-I. This is important because of the fact that the aircraft may not hold its altitude immediately after the switch PS-I closes,

sinceraisin'g the; VwheelsLand' wing aps will usually bring. about an. adjusted trim condition of the aircraft controls.. At.. this timethe two lowermost ccntactors-of relay RE-I are in the up.- ward position to close circuits between terminals I and 2 and Land 5 of the terminal block 'IIB-I... This action completes the circuits required. toraise ther landing gear and the wing flaps. The latter elements are operated by means of reversible., direct current motors operating on the 24 volt D. C. source available on the aircraft. The selector gangglh.r makes exactly the same connections asdescribed yin the preceding paragraph.. to maintain theI climb condition of the aircraft.

3. When the aircraft has reached the 4000 foot; cruise altitudethe aneroid switch PS-Z closes, thusy energizing the holding coil of relay RE-Z and through this relay closing a circuit from ground to` point 2 of the selector gang le. The brush 4e being connected to the stepping circuit/relay holding coil,v the relay is operated to close the stepping circuit solenoid circuit and once again step theselector which will now be at point 3, Ytobegin the4 cruise phase of the night plan. YThe. gang lo continues to hold the relay REI in the upward position, while gang lc similarly acts tohold the relay RE-Z in the upward position regardless of the circuit closed by the aneroid switch PS-Z. Thev gang Id through relay RE-I` acts to connect the-constant altitudev control unt of theV auto-pilot, which takes effect at any altitude at which it isturned on to hold the aircraft in level flight at that altitude- The selector gang Ig closesacircuit to the holding coil of relay REL-I5, thusclosing the relay upwardly and completing a circuit from the automatic approach coupling AAC. to the synchro-control transformer SCT., The latter is connected to the gyra-compass repeater associated with the autopilot and isV similar in construction to a selfsynchronous unitexcpt that the rotor is relatively stationary with respect to the stator. The rotor can however bepre-set in any rotative position to provide a desired magnetic heading signal forl the auto-pilot, the signal being fed from the synchro-control transformer rotor through the automatic approach coupling and intothe automatic-pilot. The pre-set heading in the present example is selected to direct the aircraft toward the first radio compass station (or nondirectional radio beacon). The relay RE-I5 alsor connects the air log spinner ALS to the air log counter ALC. The counter unit ALC includes a counter-stepping circuit. which is actuated a number of times during each air mile by a contact arrangementv in the air log spinner unit, the latter being driven by a propeller located in the air stream outside the aircraft structure. It is also noted that selector gang lz' closes a circuit from trunk line I5 connected to terminal 2 of terminal block TB-Z to trunk line I3 connected through relay RE-I'r to terminal I of terminal block TB2. The purpose of this connection will be explained below under the section entitled Automatic pilot.

4. When la pre-set mileage has run out the cruise phase-of the ight is almost complete, and the air log contact wheel ALCW closes a circuit from ground to the trunk line I0 and thence to point' 3 on gang Ieto operate the selector stepping circuit and move the sequence selector to point 4. At this Apoint the gang Ib will continue to hold the relay RE-I in the upward position. The gang Ic acts through the trunk line 5 to complete a circuit to the heating coil or other 13 timing circuit of time delay relay TR-I. The relay TR-I being normally open, the relay RE-B will be in the downward position until the timing circuit of relay TR-I takes effect in four seconds to close the holding coil circuit of relay REI-6. Thus immediately on reaching point 4 the gang I will complete a circuit through trunk line 3 and relay RE-B to the holding coil of relay RE-IU. The latter relay then closes the tuning circuit TC-I forming a tuning channel of the radio compass tuner previously mentioned and further referred to below under the section entitled Radio compass. The radio compass is thus tuned automatically to the frequency of the first radio compass station. After fourseconds the timing circuit of time delay relay TPV-I acts to close the relay and energize the holding coil of relay RE-6, the latter taking an upward position and breaking the circuit to the holding coil of relay RE-II'I. The latter relay assumes its downward position, thus breaking the compass tuning circuit 'IC-I. It is of course understood that the tuning of the compass will be undisturbed until another compass tuning circuit is energized. The radio compass output is connected to the automatic approach coupling unit of the auto-pilot by means of the radio compass relay RCR, which takes effect at point 4 of selector gang Iy. The complete relay and connections for the relays RCR, LRR and GPRR are not shown, but it is understood that energizing of the relay -holding coils of relays RCR, LRR and GPRR closes circuits which connect the output signals of the radio compass, the localizer receiver and lthe glide path receiver to the automatic approach coupling. It is also noted that the selector gang Ii closes a circuit from terminal 2 of terminal block TB-Z to terminal I of the same terminal block, as in the previous paragraph. Noting again gang Ic it should be eX- plained that the trunk line 5 does not connect with the trunk line 'I vthrough relays Rit-3 and RSE-4, since the holding coil ofthe latter relay is energized when the aircraft is off the ground. The nose wheel micro-switch MS-I and the right wheel micro-switch MS-2 are both closed when the weight of the aircraft is oir the landing gear,

therefore the holding coils of relays PME-ll and RE-S are energized during free flight and the relays are in` the upward position accordingly.

5. On approaching the. location of the first non-directional radio beacon under the influence of the homing signal received therefrom, the marker beacon receiver picks up the Z-marker beacon signal and passes it through the marker vbeacon receiver coupling MBRC to be described below under a separate heading. The coupling output is Apassed by trunk line I to point 4 of gang I e to once more step the selector to a new station (point 5). The construction of the marker bea-con receiver coupling precludes further stepping of the selector at this time even though the gang Ie still makes a. connection through trunk line I to the receiver coupling. The gang Ic is now connected to the trunk line IB t-o close a Icircuit to relay RE-, and thence to the holding -coil of relay RE-I I. The latter closes .to operate the radio compass tuning circuit TC-2 and tune the radio comp-ass to the frequency of the second radio compass station. The 'same trunk line I6 extendsy to the holding coil of relay RE-Id-i`and energizing this relay cl-oses the ground connection from gang Ic to the timing rcircuit of time delay relay TPV-2. After four seconds the relay TR-Z closes, com- 14 pleting a circuit through relay RE-S to the holding coil of relay RE1. The rel-ay RE-'I now moves to the upward position to break the holding coil circuit of the tuning circuit relay RE-I I, resulting in a break in the radio compass tuning circuit TC-2. The gang Ig also makes a connectionl to the radio compass relay RCR to connect the compass output into the auto-pilot by Way of the automatic approach coupling. The selector gang Ih now makes a connection from terminal I of terminal block TB-2 by way of trunk line II and trunk line I2 to relay RE-I and to the lower or down signal -side of resistn ance bridge circuit RBC. The bridge having been pre-set for a desired signal the aircraft begins the initial approach glide, which continues at the reduced power setting obtained by Aselect-or gang I a until the aircraft reaches 1000 feet, at which time the aneroid switch PS-l opens. The switch PS-I being open the holding coil of relay RE-I becomes deenergized and the relay assumes its downward position. This makes a circuit from gang ld to the constant altitude control unit of the auto-pilot, so that the aircraft levels off at the corresponding altitude (1000 feet in this example). The relay RE-I also makes connections between terminals 2 and 3, and -5 and B of the terminal block TB-I thus connecting the motors for the landing gear and wing flaps to lower these elements. The relay RE-I breaks the connection to the down signal portion of resist-ance bridge circuit RBC, and by means of selector gang Ii now makes a connection through trunk lines I4 and I5 across the terminals I Iand 2 of the auto-pilot terminal block TB-Z.

6. Continuing the night at about 1000 feet of altitude with -a heading directly toward the second n-ondirectional radio beacon the 4aircraft comes in over the beacon (radio compass station) at which point there is an outer marker beacon radiating a balloon-shaped signal field upwardly. When the `aircraft reaches this signal field the marker beacon receiver picks up the signal and passes it to the marker beacon receiver coupling MBRC, the latter producing an impulse through gang Ie to operate the selector stepping circuit SC' Iand step the selector to point 6. At this station the gang I d makes a connection to the constant altitude control,v so as to hold the 1000 vfoot altitude in effect. The gang yIf completes a circuit through trunk line 2 thus actuating the holding coil of relay REI-I2 through relay RE-8 and operating the tuning circuit TC-3. This action merely tunes the radio compass to a new wavelength for directional control of the aircraft in the ensuing phase of the flight. In the present example this would be useful only if the aircraft is to home on a third radio compass station, located on the approach path to the landing eld. The circuits completed by gang If Iand trunk line 2 include one to the holdingA coil of relay REI-I3', the latter closing upwardly to start the timing circuit of time delay rel-ay 'IR-I. The latter closes after four seconds to energize the holding coil of relay RE- and break the tuning circuit TC-3, the frequency tuner of the radio compass having had `ample time vduring this interval to tune the gang condenser of the compass circuit. In the present aircraft control system the preferred means of directional control during .the approach phases following the second radio com -pass station is the runway-localizer control. It should be understood that the system is flexible enough to substitute the radio compass directional control for runway-localizar control. However it -is found that the loc-alizer signals carry far enough from the landing field to make possible directional control from lthe outer marker beacon oninto the field. yAs may be seen from Fig. 2a this distance may be in the neighborhood of fifteen miles, although the distances there indicated are stated .by way of eX- ample only. Since the gang lg at point V6 makes a connection to the localizer receiver relay LER, the relay closes a circuit to connect the receiver signal into the automatic approach coupling from whence the directional signal goesto the automatic pilot. The'standard localiser receiver is not modied in any way, its signal being used in the present case to giveran automatic direc-` tional control instead yof merely operating a leftright needle of an indicating device. The gang li at point 6 connects together the trunk lines I4 and l5, thus connecting the terminals l and 2 of the auto-pilot terminal block TB-2. y 1- 7. On reaching the inner marker beacon the signal emitted generally upwardly therefrom is received by the marker beacon receiver and through the marker beaconrecever coupling MBRC an impulse is passed onto the selector stepping circuit to step the selector to point '7, the impulse reaching the stepping circuit by way of the trunk line I and gang le. With the selector now at point 7 circuits are completed by the selector gangs la (power control), lf, Ic, Ii and ly' (selector station indicator). The gang lf completes a circuit to the glide path receiver relay GPRR, which closes a circuit for connection of the receiver signal to the automatic approach coupling from whence the correct down signal is fed to the automatic pilot. The standard glide path'receiver is not modified for use in the present system but its signal is used to hold the aircraft on the glide path automatically, instead of merely operating a normally horizontal needle of an indicator. The gang ig completes a circuit tothe localizer receiver relay LRR to hold the runway-localizar contr-ol, which was initiated at the beginning of flight phase 6 under the preferredv flight plan. Through gang Iz the trunk lines It and l are connected together, thus connecting terminals l` and Z of the auto-pilot terminal block TB-Z through the relay REI-I.

8. The micro-switches MS-l and MS-Z are actuated by Bowden wires connected to the folding links or nut-crackers carried on the nose wheel strut and rightrwheel strut respectively; These links Ll and L2' are shown as used on the nose wheel strut in Fig. 8. The Bowden wire connects to the link connection J so-as to be .put under tension when the links fold closer togetherl.

On touchdown of the aircraft the switches MIS-I and MS-Z are opened, this causing the holding coils of relays RE-ll and RE-5 to become deenergized. When relay REI-4 reaches the downward position thecircuitV to the heating coil of time delay relay TR-Z is completed through trunk lines 8 and 9 and relay, REFS. The relay Tft-2 closes after four seconds tov connect the contactors of relay RE-S together. Opening of microswitch MS-Z and disconnecting ofI the holding coil of relay RE-S completes a circuit to the relay of stepping circuit SCby way of relay REFS, re-` lay REf-ll, relay. RE-B and selector gang le. Closing this circuit then steps the selector to point .8 by means of the stepping circuit solenoid. lThe gang lg in this instance has a function in aircraft control, since at point` B'the trunk line 4 makes a connection to the holding coil of relay RE-3""and to ground through'selectcr gang ii. The relay holding coil now moves the relay RE- to the upward position, closing aV circuit from ground to the trunk line 'l by way vof relays RE- and RE-ll. Since line l connects to the holding coil of relay REI-9, the latter relay closes in the upward position to complete ay circuit across brake circuit terminals BR--I and BRf-Z through relay TRf-Z. The latter relay becomes closed four seconds after touchdown, as explained above. The brakes are now in the on position and the aircraft will come toa stop gradually, as will be more fully described below under the heading of Brake control. At point 8 the gang lf holds the glide path receiver by means of the glide path receiver relay GPRR. At point 8 the gang lg holds the localizer receiver by means of the localizer receiver relay LRR. The gang li connects the trunk lines I4 and l5, which as explained previously has the effect of connecting terminals i and 2 of the terminal block TB-2. The purpose of holding the glide path receiver is that the standard receiver includes an` alarm circuit adapted to produce an up signal when the aircraft 'rnoves out ofthe glide path signal field. This up signal when fed to the auto-pilot has the effect of holding the tail of the aircraft down, thus preventing nosing over and giving a smoother landing. The alarm circuit is normally present in the receiver to give a sudden upswing to the glide path indicator needle, and serve as a warning that the aircraft has strayed from the correct glide path. In the present system the alarm circuit signal is utilized onlyV to give an up signal to the auto-pilot after landing of the aircraft and after the aircraft has rolled past the glide path station (Fig. 2a) where it-will be out of the glide path signal field. Moreover if it should with adjustment means, so that the cruise and intermediate altitudes may be changed within liimits. This is especially useful when the aircraft is on an extended series of flights and making use of air fields having various altitudes above sea level. The switch setting dials, pref-v erably located on thecontrol system panel, may

Y be calibrated in millibars or any suitable pressure phase of the flight is necessary. The time delay' relays Tft-l and TR-Z may have any reasonable time factor, but the four second timing above described has been found'very satisfactory under average conditions where4 the control system is employed on a C-54 transport. Before use of the control system all electricr power sources are The manual switch SVV-2 is adapted to` turnedon and all vacuum tube circuits are connected to the proper sources, so that the tubes supply to the =radio compass, the marker beacon receiver, the localizer receiver and the glide path receiver, even though the signals therefrom are not utilized except at specified times.l In passing it mightbe noted that the receiving antennas for the localizer receiver, the glide path receiver and the'marker beacon receiver are designated in Fig. 8 at LRA,GPRA and MBRA respectively. In the same view there is alsoshown the radio compass loop RCL andthe radio compass sense antenna RCSA. In the circuits .as covered by Figs. 3 and 3a, as well as in other circuits shown in the drawings, .theparts indicated as connected to ground are tied to the metal framework of the aircraft. Also one side of the electric power sources are similarly grounded. Thus in connecting any part of the. system to power,'only a single line to the power source isrequired plus another line to any portion of the metal aircraft framework.

Power control The powercontrol portion of the present system is illustrated diagrammatically in Fig. 4, and theautomatic air speed control unit of Fig. 4 is shown in detail in Fig. 6. It should be understood that the power control as illustrated and described is applicable to a plurality of engines or combustion motors, even though described in connection with a single engine D adapted to drive a propeller E. When more than one engine 'is used-the control system is preferably duplicated for each engine, so that the separate power units are independent except for an engine synchronizer which is usually employed on multi-motor aircraft.

. Thev power control may be divided roughly into six parts as follows: the motor unit F, the pressuretrol G, the signal control unit H, the power selector I, the automatic air speed control J, and the selector gang Ia. The selector gang Ia forms the rst gang of the master sequence selector I (see Fig. 3), the various power selections being set into the power vselector I as the night proceeds. The comparative values for the power settings at each phase of the flight have been stated 'previously in terms of the manifold pressure.

The motor unit F includes a throttle servomotor IU and a motor follow-up potentiometer II. The motor IIJ is a two-phase reversible induction motor of the squirrel-cage type, and has two field windings as indicated in Fig. 4. The rotor of the servomoto-r is mechanically connectedby suitable reduction gearing to the follow-up potentiometer I I and tothe throttle cable control wheel I2. A substantial gear reduction is used between thev motorA I and the driven elements II and I2, so that a very small motor may beused. A suggested ratio between the motor and the driven elements is 1500 to 1, although this may vary widely according to the motor design and relative proportions of the parts to be driven.

Inorder to permit movement of the cable I3 independently of the motor and gearing when the manual throttle control (not shown) is to be operated, the throttle cable contro-1 wheel I2 is l made of two concentric sections having a clutch means for combined rotation of the sections. The clutch means may comprise spring detents slidably mounted within the inner section and env*guageable with notches formed on the inside edge amasar 18 ofthe outer section. This simple drive clutch will permit the control cable I3 to be moved without operation of the servomotor and gearing. and will also provide anadequate driving connection for the cable from the servomotor.

The cable I3 extends over and around the pulleys or quadrants I4 and I5, the pulley I4 being mounted onv the throttle valve shaft I6 adjacent to the carburetor I'I. TheA air and combustible fuel is taken into the engine through conduit I8, through the blower I9 and then intothe intake manifolds 20 leading to the engine cylinders. The

.blower unit I9 beingr geared to the engine -invcreases in speed as the engine speeds up to augment the suction effect of the moving pistons of the engine.l As vthe throttle valve is opened` up the intake ofv air increases in volume andthe quantity of fuelV drawn from the carburetor I-I increasesA proportionately,v thus stepping up the speed and the power output of theengine D. In communication with the manifold 20 is ya pressure sensitive device termed-pressuretrol G. The

ypressuretrol includes a motion-increasing lever Aratio control potentiometer 2:3, the power selection relay 24, the manual power selector 25,. the sequence selector gangv I d, and the power transformers 26 and 21. Thevarious potentiometers and resistors above named providesignal potentials which are amplified and transmitted to the `motor' I0, to produce the resultant motor rota-- tion. As each tap of the power selection resistor or voltage divider 22 is selected the manifold pressure changes until the voltage introduced from that source is balanced out by the voltage produced by the pressuretrolpotentiometer 2|. The throttle setting then. has reached a steady state and changes very little until the electrical balance is disturbed. l

Considering the circuit in detail the transformer 2l is supplied with 115 volt alternating current. The transformer output provides reduced potentials for the motorvfollow-upI po tentiometer II and for the pressuretrol potentiometer 2 I. The wiper connection of the potentiometer I I feeds a signal to the control unit H tending to cancel the `signal producing the motor and potentiometer movement, `whereby the potentiometer signal was developed. Thus the'follow-up potentiometer acts to prevent over travel of the motor, vsince at the time the potentiometer movement is suii'icient to make the two signals equal and opposite the control unit output to the servomotor cuts off and the motor stops.

The power'selection resistor or voltage divider 22 having an A. C. source in parallel therewith is provided with a series of taps each connected to a movable contactor of relay 24. The relay contactors have an upper position where they are held by a tension spring, and-a lower position where they are held by the holding coil of relay 24. In the lower position four of the taps are connected to contacts of manual power selector 25; In the upper position the taps are connected to points on sequence selector gang Ila through which they make a connection to ground. The 

